Capillary immunoassay and device therefor comprising mobilizable particulate labelled reagents

ABSTRACT

An analytical test device useful for example in pregnancy testing, includes a hollow casing (500) constructed of moisture-impervious solid material, such as plastics materials, containing a dry porous carrier (510) which communicates indirectly with the exterior of the casing via a bibulous sample receiving member (506) which protrudes from the casing such that a liquid test sample can be applied to the receiving member and permeate therefrom to the porous carrier, the carrier containing in a first zone a labelled specific binding reagent is freely mobile within the porous carrier when in the moist state, and in a second zone spatially distinct from the first zone unlabelled specific binding reagent for the same analyte which unlabelled reagent is permanently immobilised on the carrier material and is therefore not mobile in the moist state, the two zones being arranged such that liquid sample applied to the porous carrier can permeate via the first zone into the second zone, and the device incorporating an aperture (508) in the casing, enabling the extent (if any) to which the labelled reagent becomes bound in the second zone to be observed. Preferably the device includes a removable cap for the protruding bibulous member.

This is a continuation of application Ser. No. 07/876,449 filed on Apr.30, 1992, which was abandoned upon filing hereof, which is a Divisionalof Appln. Ser. No. 07/795,266 filed Nov. 19, 1991, now abandoned whichis a continuation of Appln. Ser. No. 07/294,146, filed asPCT/GB88/00322, Apr. 26, 1988, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to assays involving specific binding,especially immunoassays.

In particular, he invention relates to analytical devices which aresuitable for use in the home, clinic or doctor's surgery and which areintended to give an analytical result which is rapid and which requiresthe minimum degree of skill and involvement from the user.

2. Description of the Related Art The use of test devices in the home totest for pregnancy and fertile period (ovulation) is now commonplace,and a wide variety of test devices and kits are available commercially.Without exception, the commercially-available devices all require theuser to perform a sequence of operations before the test result isobservable. These operations necessarily involve time, and introduce thepossibility of error.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a test device whichis readily usable by an unskilled person and which preferably merelyrequires that some portion of the device is contacted with the sample(e.g. a urine stream in the case of a pregnancy or ovulation test) andthereafter no further actions are required by the user before ananalytical result can be observed. Ideally the analytical result shouldbe observable within a matter of minutes following sample application,e.g. ten minutes or less.

The use of reagent-impregnated test strips in specific binding assays,such as immunoassays, has previously been proposed. In such procedures asample is applied to one portion of the test strip and is allowed topermeate through the strip material, usually with the aid of an elutingsolvent such as water. In so doing, the sample progresses into orthrough a detection zone in the test strip wherein a specific bindingreagent for an analyte suspected of being in the sample is immobilised.Analyte present in the sample can therefore become bound within thedetection zone. The extent to which the analyte becomes bound in thatzone can be determined with the aid of labelled reagents which can alsobe incorporated in the test strip or applied thereto subsequently.Examples of prior proposals utilising these principles are given inThyroid Diagnostics Inc GB 1589234, Boots-Celltech Diagnostics LimitedEP 0225054, Syntex (USA) Inc EP 0183442, and Behringwerke AG EP 0186799.

The present invention is concerned with adapting and improving the knowntechniques, such as those referred to in the above publications, toprovide diagnostic test devices especially suitable for home use whichare quick and convenient to use and which require the user to perform asfew actions as possible.

A typical embodiment of the invention is an analytical test devicecomprising a hollow casing constructed of moisture-impervious solidmaterial containing a dry porous carrier which communicates directly orindirectly with the exterior of the casing such that a liquid testsample can be applied to the porous carrier, the device also containinga labelled specific binding reagent for an analyte which labelledspecific binding reagent is freely mobile within the porous carrier whenin the moist state, and unlabelled specific binding reagent for the sameanalyte which unlabelled reagent is permanently immobilised in adetection zone on the carrier material and is therefore not mobile inthe moist state, the relative positioning of the labelled reagent anddetection zone being such that liquid sample applied to the device canpick up labelled reagent and thereafter permeate into the detectionzone, and the device incorporating means enabling the extent (if any) towhich the labelled reagent becomes in the detection zone to be observed.

Another embodiment of the invention is a device for use in an assay foran analyte, incorporating a porous solid phase material carrying in afirst zone a labelled reagent which is retained in the first zone whilethe porous material is in the dry state but is free to migrate throughthe porous material when the porous material is moistened, for exampleby the application of an aqueous liquid sample suspected of containingthe analyte, the porous material carrying in a second zone, which isspatially distinct from the first zone, an unlabelled specific bindingreagent having specificity for the analyte, and which is capable ofparticipating with the labelled reagent in either a "sandwich" or a"competition" reaction, the unlabelled specific binding reagent beingfirmly immobilised on the porous material such that it is not free tomigrate when the porous material is in the moist state.

The invention also provides an analytical method in which a device asset forth in the proceeding paragraph is contacted with an aqueousliquid sample suspected of containing the analyte, such that the samplepermeates by capillary action through the porous solid phase materialvia the first zone into the second zone and the labelled reagentmigrates therewith from the first zone to the second zone, the presenceof analyte in the sample being determined by observing the extent (ifany) to which the labelled reagent becomes bound in the second zone.

In one embodiment of the invention, the labelled reagent is a specificbinding partner for the analyte. The labelled reagent, the analyte (ifpresent) and the immobilised unlabelled specific binding reagentcooperate together in a "sandwich" reaction. This results in thelabelled reagent being bound in the second zone if analyte is present inthe sample. The two binding reagents must have specificities fordifferent epitopes on the analyte.

In another-embodiment of the invention, the labelled reagent is eitherthe analyte itself which has been conjugated with a label, or is ananalyte analogue, ie a chemical entity having the identical specificbinding characteristics as the analyte, and which similarly has beenconjugated with a label. In the latter case, it is preferable that theproperties of the analyte analogue which influence its solubility ordispersibility in an aqueous liquid sample and its ability to migratethrough the moist porous solid phase material should be identical tothose of the analyte itself, or at least very closely similar. In thissecond embodiment, the labelled analyte or analyte analogue will migratethrough the porous solid phase material into the second zone and bindwith the immobolised reagent. Any analyte present in the sample willcompete with the labelled reagent in this binding reaction. Suchcompetition will result in a reduction in the amount of labelled reagentbinding in the second zone, and a consequent decrease in the intensityof the signal observed in the second zone in comparison with the signalthat is observed in the absence of analyte in the sample.

An important preferred embodiment of the invention is the selection ofnitrocellulose as the carrier material. This has considerable advantageover conventional strip materials, such as paper, because it has anatural ability to bind proteins without requiring prior sensitisation.Specific binding reagents, such as immunoglobulins, can be applieddirectly to nitrocellulose and immobilised thereon. No chemicaltreatment is required which might interfere with the essential specificbinding activity of the reagent. Unused binding sites on thenitrocellulose can thereafter be blocked using simple materials, such aspolyvinylalcohol. Moreover, nitrocellulose is readily available in arange of pore sizes and this facilitates the selection of a carriermaterial to suit particularly requirements such as sample flow rate.

Another important preferred embodiment of the invention is the use of socalled "direct labels", attached to one of the specific bindingreagents. Direct labels such as gold sols and dye sols, are alreadyknown per se. They can be used to produce an instant analytical resultwithout the need to add further reagents in order to develop adetectable signal. They are robust and stable and can therefore be usedreadily in a analytical device which is stored in the dry state. Theirrelease on contact with an aqueous sample can be modulated, for exampleby the use of soluble glazes.

An important aspect of the invention is the selection of technicalfeatures which enable a direct labelled specific binding reagent to beused in a carrier.-based analytical device, e.g. one based on a stripformat, to give a quick and clear result. Ideally, the result of theassay should be discernable by eye and to facilitate this, it isnecessary for the direct label to become concentrated in the detectionzone. To achieve this, the direct labelled reagent should betransportable easily and rapidly by the developing liquid. Furthermore,it is preferable that the whole of the developing sample liquid isdirected through a comparatively small detection zone in order that theprobability of an observable result being obtained in increased.

Another important aspect of the invention is the use of a directlylabelled specific binding reagent on a carrier material comprisingnitrocellulose. Preferably the nitrocellulose has a pore size of atleast one micron. Preferably the nitrocellulose has a pore size notgreater than about 20 microns. In a particularly preferred embodiment,the direct label is a coloured latex particle of spherical ornear-spherical shape and having a maximum diameter of not greater thanabout 0.5 micron. An ideal size range for such particles is from about0.05 to about 0.5 microns.

In a further embodiment of the present invention, the porous solid phasematerial is linked to a porous receiving member to which the liquidsample can be applied and from which the sample can permeate into theporous solid phase material. Preferably, the porous solid phase materialis contained within a moisture-impermeable casing or housing and theporous receiving member, with which the porous solid phase material islinked, extends out of the housing and can act as a means for permittinga liquid sample to enter the housing and permeate the porous solid phasematerial. The housing should be provided with means, e.g. appropriatelyplaced apertures, which enable the second zone of the porous solid phasematerial (carrying the immobilised unlabelled specific binding reagent)to be observable from outside the housing so that the result of theassay can be observed. If desired, the housing may also be provided withfurther means which enable a further zone of the porous solid phasematerial to be observed from outside the housing and which further zoneincorporates control reagents which enable an indication to be given asto whether the assay procedure has been completed. Preferably thehousing is provided with a removable cap or shroud which can protect theprotruding porous receiving member during storage before use. Ifdesired, the cap or shroud can be replaced over the protruding porousreceiving member, after sample application, while the assay procedure isbeing performed. Optionally, the labelled reagent can be incorporatedelsewhere within the device, e.g. in the bibulous sample collectionmember, but this is not preferred.

An important embodiment of the invention is a pregnancy testing devicecomprising a hollow elongated casing containing a dry porousnitrocellulose carrier which communicates indirectly with the exteriorof the casing via a bibulous urine receiving member which protrudes fromthe casing and which can act as a reservoir from which urine is releasedinto the porous carrier, the carrier containing in a first zone ahighly-specific anti-hCG antibody bearing a coloured "direct" label, thelabelled antibody being freely mobile within the porous carrier when inthe moist state, and in a second zone spatially distinct from the firstzone an highly-specific unlabelled anti-hCG antibody which ispermanently immobilised on the carrier material and is therefore notmobile in the moist state, the labelled and unlabelled antibodies havingspecificities for different hCG epitopes, the two zones being arrangedsuch that a urine sample applied to the porous carrier can permeate viathe first zone into the second zone, and the casing being constructed ofopaque or translucent material incorporating at least one aperturethrough which the analytical result may be observed, together with aremovable and replaceable cover for the protruding bibulous urinereceiving member. A fertile period prediction device, essentially asjust defined except that the analyte is LH, is an important alternative.

Such devices can be provided as kits suitable for home use, comprising aplurality (e.g. two) of devices individually wrapped in moistureimpervious wrapping and packaged together with appropriate instructionsto the user.

The porous sample receiving member can be made from any bibulous, porousor fibrous material capable of absorbing liquid rapidly. The porosity ofthe material can be unidirectional (is with pores or fibres runningwholly or predominantly parallel to an axis of the member) ormultidirectional (omnidirectional, so that the member has an amorphoussponge-like structure). Porous plastics material, such as polypropylene,polyethylene (preferably of very high molecular weight), polyvinylideneflouride, ethylene vinylacetate, acrylonitrile andpolytetrafluoro-ethylene can be used. It can be advantageous topre-treat the member with a surface-active agent during manufacture, asthis can reduce any inherent hydrophobicity in the member and thereforeenhance its ability to take up and deliver a moist sample rapidly andefficiently. Porous sample receiving members can also be made from paperor other cellulosic materials, such as nitro-cellulose. Materials thatare now used in the nibs of so-called fibre tipped pens are particularlysuitable and such materials can be shaped or extruded in a variety oflengths and cross-sections appropriate in the context of the invention.Preferably the material comprising the porous receiving member should bechosen such that the porous member can be saturated with aqueous liquidwithin a matter of seconds. Preferably the material remains robust whenmoist, and for this reason paper and similar materials are lesspreferred in any embodiment wherein the porous receiving memberprotrudes from a housing. The liquid must thereafter permeate freelyfrom the porous sample receiving member into the porous solid phasematerial.

If present, the "control" zone can be designed merely to convey anunrelated signal to the user that the device has worked. For example,the control zone can be loaded with an antibody that will bind to thelabelled antibody from the first zone, e.g. an "anti-mouse" antibody ifthe labelled body is one that has been derived using a murine hybridoma,to confirm that the sample has permeated the test strip. Alternatively,the control zone can contain an anhydrous reagent that, when moistened,produces a colour change or colour formation, e.g. anhydrous coppersulphate which will turn blue when moistened by an aqueous sample. As afurther alternative, a control zone could contain immobilised analytewhich will react with excess labelled reagent from the first zone. Asthe purpose of the control zone is to indicate to the user that the testhas been completed, the control zone should be located downstream fromthe second zone in which the desired test result is recorded. A positivecontrol indicator therefore tells the user that the sample has permeatedthe required distance through the test device.

The label can be any entity the presence of which can be readilydetected. Preferably the label is a direct label, ie an entity which, inits natural state, is readily visible either to the naked eye, or withthe aid of an optical filter and/or applied stimulation, e.g. UV lightto promote fluorescence. For example, minute coloured particles, such asdye sols, metallic sols (e.g. gold), and coloured latex particles, arevery suitable. Of these options, coloured latex particles are mostpreferred. Concentration of the label into a small zone or volume shouldgive rise to a readily detectable signal, e.g. a strongly-coloured area.This can be evaluated by eye, or by instruments if desired.

Indirect labels, such as enzymes, e.g. alkaline phosphatase andhorseradish peroxidase, can be used but these usually require theaddition of one or more developing reagents such as substrates before avisible signal can be detected. Hence these are less preferred. Suchadditional reagents can be incorporated in the porous solid phasematerial or in the sample receiving member, if present, such that theydissolve or disperse in the aqueous liquid sample. Alternatively, thedeveloping reagents can be added to the sample before contact with theporous material or the porous material can be exposed to the developingreagents after the binding reaction has taken place.

Coupling of the label to the specific binding reagent can be by covalentbonding, if desired, or by hydrophobic bonding. Such techniques arecommonplace in the art, and form no part of the present invention. Inthe preferred embodiment, where the label is a direct label such as acoloured latex particle, hydrophobic bonding is preferred.

In all embodiments of the invention, it is essential that the labelledreagent migrates with the liquid sample as this progresses to thedetection zone. Preferably, the flow of sample continues beyond thedetection zone and sufficient sample is applied to the porous materialin order that this may occur, and that any excess labelled reagent fromthe first zone which does not participate in any binding reaction in thesecond zone is flushed away from the detection zone by this continuingflow. If desired, an absorbant "sink" can be provided at the distal endof the carrier material. The absorbent sink may comprise, for example,Whatman 3 MM chromatography paper, and should provide sufficientabsorptive capacity to allow any unbound conjugate to wash out of thedetection zone. As an alternative to such a sink it can be sufficient tohave a length of porous solid phase material which extends beyond thedetection zone.

The presence or intensity of the signal from the label which becomesbound in the second zone can provide a qualitative or quantitativemeasurement of analyte in the sample. A plurality of detection zonesarranged in series on the porous solid phase material, through which theaqueous liquid sample can pass progressively, can also be used toprovide a quantitative measurement of the analyte, or can be loadedindividually with different specific binding agents to provide amulti-analyte test.

The immobilised specific binding reagent in the second zone ispreferably a highly specific antibody, and more preferably a monoclonalantibody. In the embodiment of the invention involving the sandwichreaction, the labelled reagent is also preferably a highly specificantibody, and more preferably a monoclonal antibody.

Preferably the carrier material is in the form of a strip or sheet towhich the reagents are applied in spacially distinct zones, and theliquid sample is allowed to permeate through the sheet or strip from oneside or end to another.

If desired, a device according to the invention can incorporate two ormore discrete bodies of porous solid phase material, e.g. separatestrips or sheets, each carrying mobile and immobilised reagents. Thesediscrete bodies can be arranged in parallel, for example, such that asingle application of liquid sample to the device initiates sample flowin the discrete bodies simultaneously. The separate analytical resultsthat can be determined in this way can be used as control results, or ifdifferent reagents are used on the different carriers, the simultaneousdetermination of a plurality of analytes in a single sample can be made.Alternatively, multiple samples can be applied individually to an arrayof carriers and analysed simultaneously.

The material comprising the porous solid phase is preferablynitrocellulose. This has the advantage that the antibody in the secondzone can be immobilised firmly without prior chemical treatment. If theporous solid phase material comprises paper, for example, theimmobilisation of the antibody in the second zone needs to be performedby chemical coup ling using, for example, CNBr, carbonyldiimidazole, ortresyl chloride.

Following the application of the antibody to the detection zone, theremainder of the porous solid phase material should be treated to blockany remaining binding sites elsewhere. 8locking can be achieved bytreatment with protein (e.g. bovine serum albumin or milk protein), orwith polyvinylalcohol or ethanolamine, or any combination of theseagents, for example. The labelled reagent for the first zone can then bedispensed onto the dry carrier and will become mobile in the carrierwhen in the moist state. Between each of these various process steps(sensitisation, application of unlabelled reagent, blocking andapplication of the labelled reagent), the porous solid phase materialshould be dried.

To assist the free mobility of the labelled reagent when the porouscarrier is moistened with the sample, it is preferable for the labelledreagent to be applied to the carrier as a surface layer, rather thanbeing impregnated in the thickness of the carrier. This can minimiseinteraction between the carrier material and the labelled reagent. In apreferred embodiment of the invention, the carrier is pre-treated with aglazing material in the region to which the labelled reagent is to beapplied. Glazing can be achieved, for example, by depositing an aqueoussugar or cellulose solution, e.g. of sucrose or lactose, on the carrierat the relevant portion, and drying. The labelled reagent can then beapplied to the glazed portion. The remainder of the carrier materialshould not be glazed.

Preferably the porous solid phase material is nitrocellulose sheethaving a pore size of at least about 1 micron, even more preferably ofgreater than about 5 microns, and yet more preferably about 8-12microns. Very suitable nitrocellulose sheet having a nominal pore sizeof up to approximately 12 microns, is available commercially fromSchleicher and Schuell GmbH.

Preferably, the nitrocellulose sheet is "backed", e.g. with plasticssheet, to increase its handling strength. This can be manufacturedeasily by forming a thin layer of nitrocellulose on a sheet of backingmaterial. The actual pore size of the nitrocellulose when backed in thismanner will tend to be, lower than that of the corresponding unbackedmaterial.

Alternatively, a pre-formed sheet of nitrocellulose can be tightlysandwiched between two supporting sheets of solid material, e.g.plastics sheets.

It is preferable that the flow rate of an aqeous sample through theporous solid phase material should be such that in the untreatedmaterial, aqueous-liquid migrates at a rate of 1 cm in not more than 2minutes, but slower flow rates can be used if desired.

The spatial separation between the zones, and the flow ratecharacteristics of the porous carrier material, can be selected to allowadequate reaction times during which the necessary specific binding canoccur, and to allow the labelled reagent in the first zone to dissolveor disperse in the liquid sample and migrate through the carrier.Further control over these parameters can be achieved by theincorporation of viscosity modifiers (e.g. sugars and modifiedcelluloses) in the sample to slow down the reagent migration.

Preferably, the immobilised reagent in the second zone is impregnatedthroughout the thickness of the carrier in the second zone (e.g.throughout the thickness of the sheet or strip if the carrier is in thisform). Such impregnation can enhance the extent to which the immobilisedreagent can capture any analyte present in the migrating sample.

The reagents can be applied to the carrier material in a variety ofways. Various "printing" techniques have previously been proposed forapplication of liquid reagents to carriers, e.g. micro-syringes, pensusing metered pumps, direct printing and ink-jet printing, and any ofthese techniques can be used in the present context. To facilitatemanufacture, the carrier (e.g. sheet) can be treated with the reagentsand then subdivided into smaller portions (e.g. small narrow strips eachembodying the required reagent-containing zones) to provide a pluralityof identical carrier units.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective view of a strip of porous solid phase material foruse in an assay test in accordance with the invention;

FIG. 2 a perspective view of a strip of porous solid phase material foruse in an assay test in accordance with the invention;

FIG. 3 is a perspective view of a device utilizing a porous strip of thetype illustrated in FIGS. 1 and 2;

FIG. 4 is a perspective view, partially broken away, revealing a porousstrip within the device of FIG. 3;

FIG. 5 is an enlarged view of one end of the device of FIG. 3;

FIG. 6 is a perspective view of another test device according to theinvention;

FIG. 7 is a perspective view, similar to FIG. 6, but partially cut awayto reveal the porous test strip contained within the body of the device;

FIG. 8 is an exploded perspective view of an assay device in accordancewith the present invention;

FIG. 9 is a cross-sectional side elevation of the device shown in FIG.8;

FIG. 10 is an enlarged view of the porous receiving member and teststrip in the device illustrated in FIGS. 8 and 9;

FIG. 11 is a plan view of another embodiment of the invention;

FIG. 12 is a schematic cross-sectional view taken along line 12--12 inFIG. 11;

FIG. 13 is a perspective view of yet another embodiment of theinvention; and

FIG. 14 is a partially cut away view of the device of FIG. 13.

By way of example only, some preferred embodiments of the invention willnow be described in detail with reference to the accompanying drawings.

Embodiment 1

FIGS. 1 and 2 represent a typical strip of porous solid phase materialfor use in an assay test in accordance with the invention, andillustrate the underlying principle upon which the invention operates.

Referring to FIG. 1, the assay test strip 10 is seen as a rectangularstrip having (for the purpose of this description) its longitudinal axisin a vertical situation. Adjacent the lower end 11 of strip 10 is anarrow band-or zone 12 extending across the entire width of the strip. Asmall region 13 of strip 10 lies vertically below zone 12. Above zone 12is a second zone 14 lying a discrete distance up strip 10 and similarlyextending the entire width of the strip. The region 15 of strip 10between zones 12 and 14 can be of any height as long as the two zonesare separate. A further region 16 of the strip extends above zone 14,and at the top 17 of the strip is a porous pad 18 firmly linked to strip10 such that pad 18 can act as a "sink" for any liquid sample which maybe rising by capillary action through strip 10.

Zone 12 is loaded with a first antibody bearing a visible ("direct")label (e.g. coloured latex particle, dye sol or gold sol). This reagentcan freely migrate through the strip in the presence of a liquid sample.In zone 14, the strip is impregnated with a second antibody havingspecificity for a different epitope on the same analyte as the firstantibody. The second antibody is firmly immobilised on the strip.

FIG. 2 illustrate what happens when the assay strip is used in ananalytical procedure. The lower end 11 of the dry strip is contactedwith a liquid sample (not shown) which may contain the analyte to bedetermined. Capillary action causes the fluid to rise through the stripand eventually reach pad 18. In so doing, the sample traverses zone 12and the labelled antibody will dissolve or disperse in the sample andmigrate with it through the strip. While migrating towards zone 14, thelabelled antibody can bind to any analyte present in the sample. Onreaching zone 14, any analyte molecule should become bound to the secondantibody, so immobilising the labelled "sandwich" so produced. If asignificant concentration of the analyte to be determined is present inthe liquid sample, in a short period of time a distinct accumulation ofthe visible label should occur in zone 14.

As an example of an analysis to which this embodiment can be applied,the analyte can be hCG, the reagents in zones 12 and 14 can bemonoclonal antibodies to hCG which can participate in a "sandwich"reaction with hCG, and the label can be a particulate dye, a gold sol orcoloured latex particles.

Although described above in relation to a "sandwich" reaction, it willbe readily apparent to the skilled reader that this can be modified to a"competition" reaction format if desired, the labelled reagent in zone12 being the analyte or an analogue of the analyte.

An assay based on the above principles can be used to determine a widevariety of analytes by choice of appropriate specific binding reagents.The analytes can be, for example, proteins, haptens, immunoglobulins,hormones, polynucleotides, steroids, drugs, infectious disease agents(e.g. of bacterial or vital origin) such as Streptococcus, Neisseria andChlamydia. Sandwich assays, for example, may be performed for analytessuch as hCG, LH, and infectious disease agents, whereas competitionassays, for example, may be carried out for analytes such as E-3-Gestrone-3-glucyronide and P-3-G (progestrone-3-glucuronide.

The determination of the presence (if any) of more than one analyte insample can have significant clinical utility. For example, the ratio ofthe levels of apolipoproteins A₁ and B can be indicative ofsusceptibility to coronary heart disease. Similarly, the ratio of thelevels of glycated haemoglobin (HbA) to unglycated (HbAo) or total (Hb)haemoglobin can aid in the management of diabetes. Additionally it ispossible to configure tests to measure two steroids simultaneously, e.gE-3-G and P-3-G. By way of example, a dual analyte test forapolipoproteins A₁ and B may be prepared by depositing, as two spaciallydistinct zones, antibody specific for apolipoprotein A₁ throughout afirst zone and depositing a second antibody specific for apolipoproteinB, throughout the second zone of a porous carrier matrix. Following theapplication of both antibodies to each of their respective zones via asuitable application procedure (e.g. ink-jet printing, metered pump andpen, or airbrush), the remainder of the porous material should betreated with a reagent, e.g. bovine serum albumin, polyvinyl alcohol, orethanolamine, to block any remaining binding sites elsewhere. A thirdand fourth reagent, bearing a label, may then be dispensed onto the drycarrier in one or more zones near to one end of the strip, the stripbeing allowed to dry between applications of the two reagent to the samezone. Reagent 3 and Reagent 4 may comprise conjugates ofanti-apolipoprotein A₁ antibody and anti-apolipoprotein B antibodyrespectively. Both of these conjugates will become mobile in and on thecarrier when in the moist state. Reagents 3 and 4 can migrate with thesolvent flow when an aqueous sample is applied to the first end of thecarrier strip. While migrating towards the two zones further along thestrip, reagent 3 may bind any apolipoprotein A₁ present in the sampleand reagent 4 may bind any apolipoprotein B present in the sample. Onreaching the first second-antibody zone (anti-apolipoprotein A₁ antibodyzone) anti-apolipoprotein A₁ molecules should become bound to the secondantibody, immobilising the labelled `sandwich` so produced. No labelledapoliprotein B molecules will bind to this first zone. On reaching thesecond second-antibody zone (anti-apolipoprotein B antibody zone) anyapolipoprotein B molecules should become bound to the second antibody(solid-phase antibody), immobilising the labelled `sandwich` soproduced. No labelled apolipoprotein A₁ molecules will bind to thesecond zone. An accumulation of each of the direct label may occur atboth or either zones to a lesser or greater extent resulting in avisible signal at either or both of the solid phase antibody zones.Excess unbound conjugate (of both reagent 3 and reagent 4) can passfreely over the two antibody zones and will be washed into the distalend of the strip.

The development of a quantifiable colour in both of the second-antibodyzones may be assessed with an appropriate form of instrumentation,yielding a ratio of colour density between the two sites.

The determination of the presence of more than two (is multiple)analytes in any sample may have significant clinical utility. Forexample, the detection of the presence of various different serotypes ofone bacterium, or the detection of the presence of soluble serologicalmarkers in humans may be useful. By way of example, a multiple analytetest for the detection of the presence of different serotypes ofStreptococcus can be prepared for groups A, B, C and D. A cocktail ofmonoclonal antibodies, each specific for various pathologicallyimportant group serotypes, or a polyclonal antiserum raised against aparticular Streptococcal group, can be dispensed onto a porous carrierstrip as a line extending the width of the strip of approximately 1 mmzone length. Multiple lines be dispensed in spatially discrete zones,each zone containing immunochemically reactive component(s) capable ofbinding the analyte of interest. Following the application of themultiple zones, via a suitable application procedure (eg ink-jetprinting, metered pump and pen, airbrush), the remainder of the porousmaterial should be treated with a reagent (eg bovine serum albumin,polyvinylalcohol, ethanolamine) to block any remaining binding siteselsewhere. Conjugates of label, e.g. a dye sol, and eachimmunochemically-reactive component specific for each bacterial groupmay then be dispensed either onto a single zone at the bottom end of thestrip, proximal to the sample application zone, or as a series ofseparate zones.

FIGS. 3, 4 and 5 of the accompanying drawings depict a complete deviceutilising a porous strip as just described above. FIG. 3 represents thecomplete device viewed from the front, FIG. 4 shows the same devicepartially cut away to reveal the details of the strip inside, and FIG. 5shows the underside of the device.

Referring to FIG. 3, the device comprises a flat rectangular body 30 thefront face 31 of which is perforated by a circular hole or window 32which reveals the porous test strip 10 within the body. The region ofthe test strip 10 visible through the window 32 incorporates a narrowhorizontal zone 14.

Referring to FIG. 4, the device comprises a dry rectangular test strip10 made from porous material which extends from the bottom end 33 of thebody 30 within the body between the front 31 and back 34 of the body.Near the bottom end 11 of the strip 10 is a horizontal zone 12 bearing alabelled specific binding reagent for an analyte, the binding reagentbeing mobile in the test strip in the moist state. Further up the teststrip is the narrow horizontal zone 14 which is visible through thewindow 32. At the top 17 of the test strip 10 is a porous `sink` 18which can absorb any liquid sample that has permeated upwards throughthe strip.

Referring to FIG. 5, the bottom edge 35 of the body 30 incorporates alateral aperture in which the bottom end 11 of the strip lies.

In operation, the bottom end 33 of the body 30 is immersed in a liquidsample (eg urine) so that the liquid sample can be absorbed by thebottom end 11 of the test strip 20 and rise by capillary action to thetop 17 of the test strip and into the sink 18. In so doing, the liquidsample progresses via zone 12 to zone 14. Specific binding reactions asdescribed above occur, and the test result is visible to the userthrough the window 32.

Embodiment 2

FIGS. 6 and 7 of the accompanying drawings illustrate another testdevice according to the invention. FIG. 6 illustrates the completedevice viewed from the front, and FIG. 7 depicts the same devicepartially cut away to reveal details of a porous test strip containedwithin the body of the device.

Referring to FIG. 6, the device comprises an elongate body 200terminating at its lower end 201 in a small integral receptacle 202which can hold a predetermined volume of a liquid sample, eg urine. Thefront face 203 of the body 200 incorporates two square small squareapertures or windows 204 and 205 located one above the other.

Referring to FIG. 7, the elongate portion of the body 200 is hollow andincorporates a test strip 206 running almost the full height of thebody. This test strip is of similar construction to those describedunder Embodiment 1, and incorporates near its lower end 207 a horizontalzone 208 bearing a labelled specific binding reagent that can freelymigrate in the strip in the moist state. There are two circular zones209 and 210 adjacent to the windows 204 and 205 and visibletherethrough. The strip terminates at its top end 211 in a porous sink212. At the bottom end 201 of the device, the receptacle 202communicates with the hollow body via a lateral aperture 213.

In operation, a liquid sample is applied to the bottom end of the deviceand a predetermined volume of the sample fills the receptacle 202. Fromthe receptacle 202 the liquid sample rises by capillary action throughthe test strip 206 and conveys the labelled reagent from zone 208 to thetwo circular zones 209 and 210. A series of specific binding reactionsas described in relation to Embodiment 1 above occur. In this embodimentthe second circular zone 210 can act as a control (giving rise, forexample, to a coloured signal irrespective of whether or not the samplecontains the analyte to be determined) and the determination of theanalyte takes place in the first circular zone 209. The user candetermine whether the analyte is present in the sample by comparing thesignal produced in the two zones.

For example, if the test is used to determine the presence of hCG inurine during the course of a pregnancy test, the circular control zone210 can contain immobilised HCG which will bind a labelled antibodywhich is carried upwards from zone 208 by the migrating liquid sample.The same labelled antibody can engage in a `sandwich` reaction with hCGin the sample and be bound in the first circular zone 209 by anotherspecific anti-hCG antibody which has been immobilised therein.Alternatively, if desired, the "control" zone can be designed merely toconvey an unrelated signal to the user that he device has worked. Forexample, the second circular zone can be loaded with an antibody thatwill bind to the labelled antibody from zone 208, e.g. an "anti-mouse"antibody if the labelled antibody is one that has been derived using amurine hybridoma, to confirm that the sample has permeated the teststrip.

Embodiment 3

FIG. 8 of the accompanying drawings represents an isometric view of anassay device in accordance with the invention, and FIG. 9 represents across-sectional side elevation of the device shown in FIG. 8.

Referring to FIG. 8, the device comprises a housing or casing 500 ofelongate rectangular form having at one end 501 a portion 502 of reducedcross-sectional area. A cap 503 can be fitted onto portion 502 and canabut against the shoulder 504 at end 501 of the housing. Cap 503 isshown separated from housing 500. Extending beyond end 505 of portion502 is a porous member 506. When cap 503 is fitted onto portion 502 ofthe housing, it covers porous member 506. Upper face 507 of housing 500incorporates two apertures 508 and 509.

Referring to FIG. 9, it can be seen that housing 500 is of hollowconstruction. Porous member 506 extends into housing 500 and contacts astrip of porous carrier material 510. Porous member 506 and strip 510overlap to ensure that there is adequate contact between these twomaterials and that a liquid sample applied to member 506 can permeatemember 506 and progress into strip 510. Strip 510 extends further intohousing 500. Strip 510 is "backed" by a supporting strip 511 formed oftransparent moisture-impermeable plastics material. Strip 510 extendsbeyond apertures 508 and 509. Means are provided within housing 500 bywebbs 512 and 513 to hold strip 510 firmly in place. In this respect,the internal constructional details of the housing are not a significantaspect of the invention as long as the strip is held firmly in placewithin the housing, and porous member 506 is firmly retained in thehousing and adequate fluid permeable contact is maintained betweenmember 506 and strip 510. The transparent backing strip 511 lies betweenstrip 510 and apertures 508 and 509 and can act as a seal againstingress of moisture from outside the housing 500 via these apertures. Ifdesired, the residual space 514 within the housing can containmoisture-absorbant material, such as silica gel, to help maintain thestrip 510 in the dry state during storage. The reagent-containing zonesin strip 510 are not depicted in FIG. 8, but the first zone containingthe labelled reagent which is mobile when the strip is moistened willlie in the region between the porous member 506 and aperture 508. Thesecond zone containing the immobilised unlabelled reagent will lie inthe region exposed through aperture 508 in order that when the devicehas been used in an assay, the result can be observed through aperture508. Aperture 509 provides means through which a control zone containingfurther reagents which may enable the adequate permeation of samplethrough the strip to be observed.

In operation, the protective cap 503 is removed from the holder andmember 506 is exposed to a liquid sample e.g. by being placed in a urinestream in the case of a pregnancy test. After exposing member 506 to theliquid sample for a time sufficient to ensure that member 506 issaturated with the sample, the cap 503 can be replaced and the deviceplaced aside by the user for an appropriate time (e.g. two or threeminutes) while the sample permeates test strip 510 to provide theanalytical result. After the appropriate time, the user can observe thetest strip through apertures 508 and 509 and can ascertain whether theassay has been completed by observing the control zone through aperture509, and can ascertain the result of the assay by observing the secondzone through aperture 508.

During manufacture, the device can be readily assembled from, forexample, plastics material with the housing 500 being moulded in twoparts (e.g. upper and lower halves 515 and 516) which can be securelyfastened together (e.g. by ultrasonic welding) after the porous memberand test strip have been placed within one of the halves and thensandwiched between the two halves. The act of forming this sandwichconstruction can be used to `scrimp` the porous member and test striptogether to ensure adequate contact between them. Cap 503 can be mouldedas a separate complete item. If desired, apertures 508 and 509 can beprovided with transparent inserts which may insure greater securityagainst ingress of extraneous moisture from outside the housing. Byproviding a tight fit between the end 505 of housing 500 and theprotruding porous member 506, the application of sample to theprotruding member will not result in sample entering the device directlyand by-passing member 506. Member 506 therefore provides the sole routeof access for the sample to the strip within the housing, and candeliver sample to the strip in a controlled manner. The device as awhole therefore combines the functions of samples and analyser.

By using the test strip materials and reagents as hereinafter described,a device in accordance with FIGS. 8 and 9 can be produced which iseminently suitable for use as a pregnancy test kit or fertile periodtest kit for use in the home or clinic. The user merely needs to apply aurine sample to the exposed porous member and then (after optionallyreplacing the cap) can observe the test result through aperture 508within a matter of a few minutes.

Although described with particular reference to pregnancy tests andfertile period tests, it will be appreciated that the device, as justdescribed, can be used to determine the presence of a very wide varietyof analytes if appropriate reagents are incorporated in the test strip.It will be further appreciated that aperture 509 is redundant and may beomitted if the test strip does not contain any control means. Further,the general shape of the housing and cap, both in terms of their length,cross-section and other physical features, can be the subject ofconsiderable variation without departing from the spirit of theinvention.

A further option is the omission of the labelled reagent from the teststrip, this reagent being added to the sample prior to application ofthe sample to the test device. Alternatively, the labelled reagent canbe contained in the protruding porous member 506.

FIG. 10 of the accompanying drawings shows an enlarged view of theporous receiving member and test strip in the device illustrated inFIGS. 8 and 9.

The porous receiving member 506 is linked to the porous test strip 510,backed by the transparent plastics sheet 511, such that liquid can flowin the direction shown by the arrows through the porous receiving memberand into the porous strip. Test zone 517 incorporates the immobilisedspecific binding reagent, and control zone 518 contains a reagent toindicate that the sample has permeated a sufficient distance along thetest strip. A portion of the test strip surface opposite the backingstrip 511 and adjacent the porous receiving member 506, carries a glaze519 on which is deposited a layer 520 of labelled specific bindingreagent. The thickness of these two layers as depicted in FIG. 10 isgrossly exaggerated purely for the purpose of illustration. It will beappreciated that, in practice, the glaze may not form a true surfacelayer and the glazing material will penetrate the thickness of the stripto some extent. Similarly, the subsequently applied labelled reagent mayalso penetrate the strip. Nevertheless, he essential objective ofreducing any interaction between the labelled reagent and the carriermaterial forming the strip will be achieved. An aqueous sample depositedin receiving member 506 can flow therefrom among the length of strip 510and in so doing, will dissolve glaze 519 and mobilise the labelledreagent, and carry the labelled reagent along the strip and through zone517.

Embodiment 4

FIGS. 11 and 12 illustrate another embodiment of the invention, which isseen in plan view in FIG. 11 and in cross-section in FIG. 12, thecross-section being an elevation on the line 1212 seen in FIG. 11.

Referring to FIG. 11, the test device comprises a flat rectangularcasing 600 incorporating a centrally disposed rectangular aperture 601,adjacent the left hand end 602, and two further apertures 603 and 604near the mid point of the device and arranged such that apertures 601,603 and 604 lie on the central longitudinal axis of the devicecorresponding to line 1212. Although all three apertures are illustratedas being rectangular, their actual shape is not critical.

Referring to the cross-section seen in FIG. 12, the device is hollow andincorporates within it a porous sample receiving member adjacent end 602of casing 600 and lying directly beneath aperture 601. A test strip ofsimilar construction to tat described with reference to Embodiment 4,comprising a porous strip 606 backed by a transparent plastics sheet 607is also contained within casing 600, and extends from the porousreceiving member 602, with which the porous carrier is in liquidpermeable contact, to the extreme other end of the casing. Thetransparent backing sheet 607 is in firm contact with the upper innersurface 608 of casing 600, and provides a seal against apertures 603 and604 to prevent ingress of moisture or sample into the casing. Althoughnot shown in the drawings, the porous test strip 606 will incorporate alabelled specific binding reagent, and a test zone and a control zoneplaced appropriately in relation to apertures 603 and 604, in a manneranalagous to that described in Embodiment 3.

In operation, an aqueous sample can be applied through aperture 601,e.g. by means of a syringe, to saturate porous receiving member 605.Thereafter, the aqueous sample can permeate the test strip and after anappropriate time the test result can be observed through apertures 403and 604.

Embodiment 5

A yet further embodiment of the invention is illustrated in FIGS. 13 and14 of the accompanying drawings. FIG. 13 shows a device comprising arectangular casing 700 having in its upper surface 701 a rectangularaperture 702. One end wall 703 of the device 703 incorporates anaperture 704 through which a porous test element communicates with theexterior of the device. Aperture 702 is situated in surface 701 at apoint relatively remote from the end 703 containing the aperture 704.

FIG. 14 shows a partially cut-away view of the device in FIG. 13. Thehollow device incorporates a porous test strip 705, running almost theentire length of casing 700 from aperture 704. Test strip 705incorporates a first zone 706 containing a labelled specific bindingreagent ad a further zone 707, remote from aperture 704, incorporatingan immobilised specific reagent. Zone 706 lies directly beneath aperture702 is therefore observable from outside casing. Beneath strip 705 andadjacent zone 707, is a crushable element 708 containing one or moresubstrates or reagents which can be used to produce a detectable signalwhen released into zone 707, if labelled reagent from 706 has becomebound in zone 707 following use of the device. Release of the reagentsfrom member 708 can be effected by applying pressure to the outside ofthe casing at that point in order to crush the member and express thereagent therefrom.

In operation, the first test element can be exposed to an aqueoussample, e.g. by dipping end 703 of casing 700 into a vessel containingthe sample. The liquid sample will then permeate the length of teststrip 705, taking labelled reagent from zone 706 and passing throughzone 707 where the labelled reagent can become bound e.g. through a"sandwich" reaction involving an analyte in the sample. When the samplehas permeated the test strip, reagent can be released from the crushablemember 708 and the result of the test observed through aperture 702.

By way of example only, certain preferred test strip materials,reagents, and methods for their production will now be described.

1. Selection of Liquid Conductive Material

Representative examples of liquid conductive materials include paper,nitrocellulose and nylon membranes. Essential features of the materialare its ability to bind protein speed of liquid conduction; and, ifnecessary after pre-treatment, its ability to allow the passage oflabelled antibodies along the strip. It this is a direct label, it maybe desirable for the material to allow flow of particles of size up to afew microns (usually less than 0.5 μ). Examples of flow rates obtainedwith various materials are given below:

    ______________________________________                                                      Pore          Time to Flow                                                    size          45 mm (minutes)                                   ______________________________________                                        Schleicher + Schuell                                                                          3μ           3.40                                          nitrocellulose (unbacked)                                                                     5μ           3.30                                                          8μ           3.00                                                          12μ          2.20                                          polyester-backed                                                                              8μ  (nominal)                                                                              3.40                                          Whatman Nitrocellulose                                                                        5               19.20                                         Pall "Immunodyne" (nylon)                                                                     3               4.00                                                          5               3.20                                          ______________________________________                                    

The speed of a test procedure will be determined by the flow rate of thematerial employed and while any of the above materials can be used somewill give faster tests than others.

Nitrocellulose had the advantage of requiring no activation and willimmobilise proteins strongly by absorbtion. "Immunodyne" ispre-activated and requires no chemical treatment. Papers, such asWhatman 3 MM, require chemical activation with for examplecarbonyldiimidazole in order to successfully immobilise antibody.

2. Labels

Preparation of Labels

A selection of labels which may be used are described below. This listis not exhaustive.

A) Gold Sol Preparation

Gold sols may be prepared for use in immunoassay fromcommercially-available colloidal gold, and an antibody preparation suchas anti-alpha human chorionic gonadotrophin. Metallic sol labels aredescribed, for example, in European patent specification No. EP 7654.

For example, colloidal gold G20 (20 nm particle size, supplied byJanssen Life Sciences Products) is adjusted to pH 7 with 0.22 μ filtered0.1 M K₂ CO₃, and 20 mls is added to a clean glass beaker. 200 μ1 ofanti-alpha hCG antibody, prepared in 2 mM borax buffer pH 9 at 1 mg/ml,and 0.22μ filtered, is added to the gold sol, and the mixture stirredcontinuously for two minutes. 0.1M K₂ CO₃ is used to adjust the pH ofthe antibody gold sol mixture to 9, and 2 mls of 10% (w/v) BSA is added.

The antibody-gold is purified in a series of three centrifugation stepsat 12000 g, 30 minutes, and 4° C., with only the loose part of thepellet being resuspended for further use. The final pellet isresuspended in 1% (w/v) BSA in 20 mM Tris, 150 mM NaCl pH 8.2.

B) Dye Sol Preparation

Dye sols (see, for example, European patent specification No. EP 32270)may be prepared from commercially-available hydrophobic dyestuffs suchas Foron Blue SRP (Sandoz) and Resolin Blue BBLS (Bayer). For example,fifty grammes of dye is dispersed in 1 litre of distilled water bymixing on a magnetic stirrer for 2-3 minutes. Fractionation of the dyedispersion can be performed by an initial centrifugation step at 1500 gfor 10 minutes at room temperature to remove larger sol particles as asolid pellet, with the supernatant suspension being retained for furthercentrifugation.

The suspension is centrifuged at 3000 g for 10 minutes at roomtemperature, the supernatant being discarded and the pellet resuspendedin 500 mls distilled water. This procedure is repeated a further threetimes, with the final pellet being resuspended in 100 mls distilledwater.

The spectra of dye sols prepared as described above can be measured,giving lambda-max values of approximately 657 nm for Foron Blue, and 690nm for Resolin Blue. The absorbance at lambda-max, for 1 cm path length,is used as an arbitrary measure of the dye sol concentration.

C) Coloured Particles

Latex (polymer) particles for use in immunoasays are availablecommerically. These can be based on a range of synthetic polymers, suchas polystyrene, polyvinyltoluene, polystyrene-acrylic acid andpolyacrolein. The monomers used are normally water-insuluble, and areemulsified in aqueous surfactant so that monomer mycelles are formed,which are then induced to polymerise by the addition of initiator to theemulsion. Substantially sperical polymer particles are produced.

Coloured latex particles can be produced either by incorporating asuitable dye, such as anthraquinone, in the emulsion beforepolymerisation, or by colouring the pre-formed particles. In the latterroute, the dye should be dissolved in a water-immiscible solvent, such achloroform, which is then added to an aqueous suspension of the latexparticles. The particles take up the non-aqueous solvent and the dye,and can then be dried.

Preferably such latex particles have a maximum dimension of less thanabout 0.5 micron.

Coloured latex particles may be sensitised with protein, and inparticular antibody, to provide reagents for use in immunoassays. Forexample, polystyrene beads of about 0.3 micron diameter, (supplied byPolymer Laboratories) may be sensitised with anti-alpha human chorionicgonadotrophin, in the process described below:

0.5 ml (12.5 mg solids) of suspension is diluted with 1 ml of 0.1Mborate buffer pH 8.5 in an Eppendorf vial. These particles are washedfour times in borate buffer, each wash consisting of centrifugation for3 minutes at 13000 rpm in an MSE microcentrifuge at room temperature.The final pellet is resuspended in 1 ml borate buffer, mixed with 3002μg of anti-alpha hCG antibody, and the suspension is rotatedend-over-end for 16-20 hours at room temperature. The antibody-latexsuspension is centrifuged for 5 minutes at 13000 rpm, the supernatant isdiscarded and the pellet resuspended in 1.5 mls borate buffer containing0.5 milligrammes bovine serum albumin. Following rotation end-over-endfor 30 minutes at room temperature, the suspension is washed three timesin 5 mg/ml BSA in phosphate buffered saline pH 7.2, by centrifugation at13000 rpm for 5 minutes. The pellet is resuspended in 5 mg/ml BSA/5%(w/v) glycerol in phosphate buffered saline pH 7.2 and stored at 4° C.until used.

(A) Anti-hCG-Dye Sol Preparation

Protein may be coupled to dye sol in a process involving passiveadsorption. The protein may, for example, be an antibody preparationsuch as anti-alpha human chorionic gonadotrophin prepared in phosphatebuffered saline pH 7.4 at 2 milligram/mi. A reaction mixture is preparedwhich contains 100 μl antibody solution, 2 mls dye sol, 2 mls 0.1Mphosphate buffer pH 5.8 and 15.9 mls distilled water. After gentlemixing of this solution, the preparation is left for fifteen minutes atroom temperature. Excess binding sites may be blocked by the additionof, for example, bovine serum albumin: 4 mls of 150 mg/ml BSA in 5 mMNaCl pH 7.4 is added to the reaction mixture, and after 15 minutesincubation at room temperature, the solution is centrifuged at 3000 gfor 10 minutes, and the pellet resuspended in 10 mls of 0.25% (w/v)dextran/0.5% (w/v) lactose in 0.04M phosphate buffer. This antibody-dyesol conjugate is best stored in a freeze dried form.

(B) LH-Dye Sol Preparation

Due to the structural homology between the alpha subunits of hCG and LH,alpha hCG antibody can be used to detect LH in a cross-reactiveimmunoassay. Thus, a labelled antibody may be prepared for use in an LHassay in an identical manner to that described in Example 1, usinganti-alpha hCG antibody.

3. Preparation of Reagent Strip

Zonal Impregnation of Liquid-conductive Material

Liquid-conducting material with a restricted zone of immobilisedprotein, particularly antibody, can be prepared for example as follows:

A rectangular sheet of Schleicher and Schuell backed 8 μ nitrocellulosemeasuring 25 cm in length and 20 cm in width may have a reaction zoneformed upon it by applying a line of material about 1 mm wide at 5 cmintervals along its length and extending throughout its 20 cm width. Thematerial can, for example, be a suitably selected antibody preparationsuch as anti-beta (human chorionic gonadotropin of affinity Ka at 10⁹prepared in phosphate buffered saline pH 7.4 at 2 milligram/ml, suitablefor immunoassay of human chorionic gonadotrophin using a second(labelled) anti-hCG antibody in a sandwich format. This solution can bedeposited by means of a microprocessor-controlled microsyringe, whichdelivers precise volumes of reagent through a nozzle, preferably 2 mmdiameter. When the applied material has been allowed to dry for 1 hourat room temperature, excess binding sites on the nitrocellulose areblocked with an inert compound such as polyvinyl alcohol (1% w/v in 20mM Tris pH 7.4) for 30 minutes at room temperature, and sheets arethoroughly rinsed with distilled water prior to drying for 30 minutes at30° C.

In one embodiment, the liquid conductive material can then be cut upinto numerous strips 5 cm in length and 1 cm in width, each stripcarrying a limited zone of the immobilised antibody to function as animmunosorbent part way (e.g. about half way) along its length. In thisexample the test strip is used with a liquid label which is mixed withsample. In use, this limited zone then becomes a test reaction zone inwhich the immunoassay reactions take place.

In another embodiment, the label may be dispensed/deposited into/on arestricted zone before cutting up the liquid-conductive material intostrips. By way of example, this reagent may be dye sol or dyepolymer-conjugated anti-hCG antibody prepared as described under dye solpreparation, said reagent being retained in the zone when the materialis in the dry state but which is free to migrate through the carriermaterial when the material is moistened, for example, by the applicationof liquid sample containing the analyte to be determined. This mobilereagent zone is applied, for example, as follows:

A sheet of Schleicher and Schuell backed 8 μ nitrocellulose, 25 cm inlength and 20 cm in width with zones of immobilised antibody at 5 cmintervals along its length, is prepared as described previously. Priorto the deposition of dye labelled antibody, a sublayer of, for example,60% w/v of sucrose in distilled water is applied by airbrush on themicroprocessor controlled system at 6 cm intervals along the length ofthe sheet. Then several passes (e.g. three) of dye labelled antibodyprepared in 1% methacel KAM (Trademark for methylcellulose from DowChemical Company) and 0.6% (w/v) polyvinylalcohol are applied byairbrush or by microsyringe directly on top of the sublayer. Sheets arethen allowed to dry, and cut into strips 5 cm in length and 1 cm inwidth, to be used in the completed device.

Gold sols, or coloured polystyrene particles can be deposited by asimilar process.

In addition to the test zone various control zone options can beoperated. For example a zone of anti-species IgG may be deposited afterthe test zone.

4. Sandwich Assays Using Strip Format

A sandwich-type reaction may be performed for the detection of humanchorionic gonadotrophin (hCG) in a liquid sample. Preferably the labelused is a direct label which is readily visible to the naked eye. Dyesols, gold sols or coloured latex particles may be linked to anti hCGantibody, as described above.

With direct labels, assays may be performed in which fresh urine samplesare applied directly from the urine stream, or by delivering anappropriate volume (e.g. 100 μl) from a container using a pipette to theabsorbent wick of the test device. Each sample is allowed to run forfive minutes in the device, and the colour generated at the reactivezone read either by eye, or using a light reflectometer.

Indirect labels such as enzymes e.g. alkaline phosphatase may also beused, but require the addition of substrate to generate a colouredendpoint.

Enzyme assays may be performed in which the anti-hCG antibody isconjugated to alkaline phosphatase, using conventional techniques, anddiluted 1/100 in 0.01M phosphate buffered saline pH 7 containing 3%polyethylene glycol 6000, 1% (w/v) bovine serum albumin and 0.02% TRITONX305 (Trademark--obtainable from Rohm and Haas) before application tothe sheet. Fresh urine samples are then applied, either directly fromthe urine stream, or by delivering an appropriate volume (e.g. 100 μl)from a container using a pipette, to the absorbent wick of the testdevice. Each sample is allowed to run for five minutes before a pad ofliquid-swellable material soaked in BCIP substrate (at 1 mg/ml in 1MTris/HCl pH 9.8) is placed in contact with the immobile antibody zone.After a further five minutes, the pad is removed, and colour generatedread either by eye, or by using a light reflectometer.

A similar embodiment can be prepared using lutenising hormone (LH)instead of hCG.

5. Competitive Assays

A competitive type assay may be performed as exemplified byestrone-3-glucuronide, a urinary metabolite of estrone. Conjugates ofestrone-3-glucuronide and bovine serum albumin are prepared as follows:

Preparation of BSA-Estrone-3-glucuronide

The conjugation of E-3-G and BSA may be achieved through the use of amixed anhydride. All of the glassware, solvents and reagents employed inthe preparation of the activated species must be thoroughly dried usingan oven, dessicator or molecular sieves, as appropriate, for at least 24hours.

Solutions of E-3-G (2 nM) in dry dimethylformamide (DMF) andtri-n-butylamine (TnB) (10 nM) in dry DMF were equilibrated separatelyat 4° C. Using pre-cooled glassware E-3-G in DMF (1.25 ml) and TnB inDMF (0.25 ml) were added to a pre-cooled 5 ml Reactivial containing amagnetic stirrer. A solution of isobutyl chloroformate in dry DMF (10nM) was prepared and an aliquot (0.25 ml) was cooled to 4° C. and addedto the Reactivial. The contents of the Reactivial were stirred for 20minutes at 4° C. and a solution of BSA (1 mg/ml) in bicarbonate buffer(0.5%) was prepared. When the mixed anhydride incubation was complete,the contents of the Reactivial were added to the BSA solution (2.5 ml)and stirred on a magnetic stirrer for 4 hours at 4° C. The conjugatepreparation was purified by passage through a Tris buffer equilibratedPharmacia PD-10 SEPHADEX G-25 column, transferred to an amber glassstorage bottle and stored at 4° C.

Preparation of BSA-E-3-G dye Sol

A dispersion of dye (5% w/v) in distilled water was prepared withthorough mixing and aliquots were centrifuged at 3850 rpm (1500 g) for10 minutes in a bench top centrifuge. The pellet was discarded and thesupernatant was retained and centrifuged in aliquots at 4850 rpm (3000g) for 10 minutes in a bench top centrifuge. The supernatant wasdiscarded and the pellet was resuspended in half of its original volumein distilled water. This step was repeated four times to wash thepellet. The pellet was finally resuspended in distilled water and theabsorbance at lambda max was determined.

Solutions of dye sol in distilled water and E-3-G/BSA conjugate dilutedin phosphate buffer were mixed to give final concentrations of 10 μg/mlconjugate (based on BSA content) and an extrapolated dye sol opticaldensity of 20 at the absorbance maximum. The reaction mixture wasincubated for 15 minutes at room temperature and blocked for 15 minutesat room temperature with BSA in a NaCl solution (5 mM, pH 7.4 to yield afinal BSA concentration of 25 mg/ml. The reaction mixture wascentrifuged at 4850 rpm (3000 g) for 10 minutes in a bench topcentrifuge, the supernatant was discarded and the pellet was resuspendedin half of its original volume in Dextran (0.25% w/v)/Lactose (0.5% w/v)phosphate (0.04M pH 5.8 buffer.

Preparation of E-3-G Test Strips

Antibodies to E-3-G were deposited as described in example 3. BSA-E-3-Gdye sol was deposited on the strips as described in 3.

Determination of E-3-G

Using reagents described above, a standard curve can be generated byrunning strips with samples with known concentrations of E-3-G. Thecolour at the immobile zone can be read, for example using a Minoltachromameter, and the concentration of E-3-G calculated by extrapolatingfrom the reflectance value.

The invention described herein extends to all such modifications andvariations as will be apparent to the reader skilled in the art, andalso extends to combinations and subcombinations of the features of thisdescription and the accompanying drawings.

We claim:
 1. An analytical test device for detecting an analytesuspected of being present in a liquid biological sample, said devicecomprising:a) a hollow casing having a liquid biological sampleapplication aperture and means permitting observation of a test result;b) a test strip comprising a dry porous carrier contained within saidhollow casing, said carrier communicating directly or indirectly withthe exterior of said hollow casing through said liquid biological sampleapplication aperture to receive applied liquid biological sample, saidcarrier having a test result zone observable via said means permittingobservation, said test strip, in the dry unused state, containing alabelled reagent capable of specifically binding with said analyte toform a first complex of said labelled reagent and said analyte, saidlabel being a particulate direct label, wherein said labelled reagent isdry on said test strip prior to use and is released into mobile form bysaid applied liquid biological sample, wherein mobility of said labelledreagent within said test strip is facilitated by at least one of 1)coating at least a portion of said test strip upstream from said testresult zone with, or 2) drying said labelled reagent onto a portion ofsaid test strip upstream from said test result zone in the presence of,a material comprising a sugar, in an amount effective to reduceinteraction between said test strip and said labelled reagent; saidcarrier containing in said test result zone a means for binding saidfirst complex, said means for binding comprising specific binding meansand being immobilized in said test result zone; migration of saidapplied liquid biological sample through said dry porous carrierconveying by capillarity said first complex to said test result zone ofsaid dry porous carrier whereat said binding means binds said firstcomplex thereby to form a second complex; said second complex beingobservable via said means permitting observation, thereby to indicatethe presence of said analyte in said liquid biological sample.
 2. Thedevice according to claim 1, wherein said label is selected from thegroup consisting of dye sols and metallic sols.
 3. The device accordingto claim 1, wherein said labelled reagent comprises an anti-hCG antibodyand said liquid biological sample is urine.
 4. The device according toclaim 1, wherein said labelled reagent comprises an anti-LH antibody andsaid liquid biological sample is urine.
 5. The test device according toclaim 1, wherein said dry porous carrier material is nitrocellulose. 6.The test device according to claim 5, wherein said nitrocellulose has apore size greater than about 5 microns.
 7. The test device according toclaim 5, wherein said nitrocellulose has a pore size of about 8-12microns.
 8. The test device according to claim 1 which further comprisesa control zone downstream from said test result zone in said dry porouscarrier to indicate that said liquid biological sample is conveyed bycapillarity beyond said test result zone, and a control zone observationaperture in said casing, said control zone also being observable fromoutside said hollow casing through said control zone observationaperture.
 9. The test device according to claim 8, wherein said controlzone contains a means for binding said labelled reagent which comprisesspecific binding means and is immobilized in said control zone.
 10. Thetest device according to claim 1, further comprising an absorbent sinkat a distal end of said dry porous carrier, said sink having sufficientabsorptive capacity to absorb any labelled reagent not bound to saidanalyte washed out of said test zone.
 11. The test device according toclaim 1, wherein said means for binding is impregnated throughout saiddry porous carrier in said test zone.
 12. The device according to claim1, wherein said means for binding binds directly with said firstcomplex.
 13. The test device as in claim 1, wherein said meanspermitting observation comprises a test result observation aperturedefined through a wall of said casing.
 14. The test device according toclaim 1, wherein said material further comprises a protein.
 15. The testdevice according to claim 14, wherein said protein is bovine serumalbumin.
 16. The test device according to claim 1, wherein said sugar isselected from the group consisting of sucrose, lactose and dextran. 17.The test device according to claim 1, wherein mobility of said labelledreagent within said test strip is further facilitated by blocking excessbinding sites within said test strip with polyvinyl alcohol.
 18. Thetest device according to claim 1, wherein mobility of said labelledreagent within said test strip is further facilitated by blocking excessbinding sites within said test strip with a protein.
 19. The test deviceaccording to claim 18, wherein said protein is selected from the groupconsisting of bovine serum albumin and milk protein.
 20. An analyticalmethod comprising:contacting an analytical test device for detecting ananalyte suspected of being present in a liquid biological sample, saiddevice including:a) a hollow casing having a liquid biological sampleapplication aperture and means permitting observation of a test result;b) a test strip comprising a dry porous carrier contained within saidhollow casing, said carrier communicating directly or indirectly withthe exterior of said hollow casing through said liquid biological sampleapplication aperture to receive applied liquid biological sample, saidcarrier having a test result zone observable via said means permittingobservation, said test strip, in the dry unused state, containing alabelled reagent capable of specifically binding with said analyte toform a first complex of said labelled reagent and said analyte, saidlabel being a particulate direct label, wherein said labelled reagent isdry on said test strip prior to use and is released into mobile form bysaid applied liquid biological sample, wherein mobility of said labelledreagent within said test strip is facilitated by at least one of 1)coating at least a portion of said test strip upstream from said testresult zone with, or 2) drying said labelled reagent onto a portion ofsaid test strip upstream from said test result zone in the presence of,a material comprising a sugar, in an amount effective to reduceinteraction between said test strip and said labelled reagent; saidcarrier containing in said test result zone a means for binding saidfirst complex, said means for binding comprising specific binding meansand being immobilized in said test result zone; migration of saidapplied liquid biological sample through said dry porous carrierconveying by capillarity said first complex to said test result zone ofsaid dry porous carrier whereat said binding means binds said firstcomplex thereby to form a second complex; said second complex beingobservable via said means permitting observation, thereby to indicatethe presence of said analyte in said liquid biological sample, with saidliquid biological sample suspected of containing said analyte; allowingsaid liquid biological sample to convey by capillary action through saiddry porous carrier into said test result zone and said labelled reagentis conveyed therewith; and detecting the presence of said analyte insaid liquid biological sample by observing the presence of any labelledreagent-analyte complex bound in said test result zone.
 21. The methodaccording to claim 20, wherein said dry porous carrier is a strip of dryporous material, and has a control zone downstream from said test resultzone, to indicate to a user that the test has been completed; and saidhollow casing has a second observation aperture through which saidcontrol zone is visible and wherein said liquid biological sample is aurine sample whereby urine is conveyed by capillarity through said dryporous carrier into said test result zone and said control zone, andsaid test result is obtained by observing the extent to which saidlabelled reagent-analyte complex becomes bound in said test result zone.22. The method according to claim 21, wherein said control zone containsa means for binding said labelled reagent which comprises specificbinding means and is immobilized in said control zone.
 23. The methodaccording to claim 20, wherein said material further comprises aprotein.
 24. The method according to claim 23, wherein said protein isbovine serum albumin.
 25. The method according to claim 20, wherein saidsugar is selected from the group consisting of sucrose, lactose anddextran.
 26. The method according to claim 20, wherein mobility of saidlabelled reagent within said test strip is further facilitated byblocking excess binding sites within said test strip with polyvinylalcohol.
 27. The method according to claim 20, wherein mobility of saidlabelled reagent within said test strip is further facilitated byblocking excess binding sites within said test strip with a protein. 28.The method according to claim 27, wherein said protein is selected fromthe group consisting of bovine serum albumin and milk protein.
 29. Ananalytical test device for detecting an analyte suspected of beingpresent in a liquid biological sample, said device comprising:a) ahollow casing having a liquid biological sample aperture, a test resultobservation aperture, and a control zone observation aperture; b) a teststrip comprising a dry porous carrier contained within said hollowcasing, said carrier communicating directly or indirectly with theexterior of said hollow casing through said liquid biological sampleaperture to receive applied liquid biological sample, said carrierhaving a test result zone observable through said test resultobservation aperture and a control zone observable through said controlzone observation aperture, said test strip, in the dry unused state,containing a labelled reagent capable of specifically binding with saidanalyte to form a first complex of said labelled reagent and saidanalyte, said label being a particulate direct label, wherein saidlabelled reagent is dry on said test strip prior to use and is releasedinto mobile form by said applied liquid biological sample; c) anabsorbent sink at a distal end of said dry porous carrier, said sinkhaving sufficient absorptive capacity to allow any labelled reagent notbound to said analyte to wash out of said test zone; said carriercontaining in said test result zone a means for binding said firstcomplex, said means for binding said first complex comprising specificbinding means and being immobilized in said test result zone, saidcarrier containing in said control zone a means for binding saidlabelled reagent, said means for binding said labelled reagent beingimmobilized in said control zone, wherein mobility of said labelledreagent within said test strip is facilitated by at least one of 1)coating at least a portion of said test strip upstream from said testresult zone with, or 2) drying said labelled reagent onto a portion ofsaid test strip upstream from said test result zone in the presence of,a material comprising a sugar, in an amount effective to reduceinteraction between said test strip and said labelled reagent; migrationof said applied liquid biological sample through said dry porous carrierconveying by capillarity said first complex to said test result zone ofsaid dry porous carrier whereat said means for binding said firstcomplex binds said first complex, thereby to form a second complex; saidsecond complex being observable through said test result observationaperture, thereby to indicate the presence of said analyte in saidliquid biological sample.
 30. The test device according to claim 29,wherein said control zone contains a means for binding said labelledreagent which comprises specific binding means and is immobilized insaid control zone.
 31. The method according to claim 29, wherein saidmaterial further comprises a protein.
 32. The method according to claim31, wherein said protein is bovine serum albumin.
 33. The test deviceaccording to claim 29, wherein said sugar is selected from the groupconsisting of sucrose, lactose and dextran.
 34. The test deviceaccording to claim 29, wherein mobility of said labelled reagent withinsaid test strip is further facilitated by blocking excess binding siteswithin said test strip with polyvinyl alcohol.
 35. The test deviceaccording to claim 29, wherein mobility of said labelled reagent withinsaid test strip is further facilitated by blocking excess binding siteswithin said test strip with a protein.
 36. The test device according toclaim 35, wherein said protein is selected from the group consisting ofbovine serum albumin and milk protein.